The present invention relates to a method and apparatus for activating a moving web, such as a web of interconnected disposable absorbent articles, including disposable absorbent articles such as diapers, adult incontinence products, sanitary napkins and the like. More particularly, the invention relates to a method and apparatus for activating a moving web at a low strain rate while maintaining the line speed of the moving web.
U.S. Pat. No. 4,834,741 issued to Sabee on May 30, 1989 discloses a single use garment, such a disposable diaper, comprising an untensioned elastomeric element secured between a pair of drawable elements in the waistband and legband portions. The elastic elements are affixed in the waistband portions of the diaper web while in a substantially relaxed condition to a drawable topsheet web, a drawable backsheet web or both. The portions of the diaper web containing the elastic elements are thereafter laterally stretched in the cross-machine direction by the meshing corrugations located on pairs of corrugated rolls. Simultaneously the coinciding portions of the drawable topsheet and backsheet webs in the area of the elastic element are incrementally stretched and drawn to impart a permanent elongation and molecular orientation thereto in the cross-machine direction. Because the corrugated rolls have their meshing corrugations aligned substantially parallel to the machine direction, the incremental stretching of the web takes place in the cross-machine direction. Accordingly, the fully processed waistband portions of the diaper web are thereafter elastically extensible in the cross-machine direction, at least to the point of initial stretching.
A similar operation is carried out with respect to the legbands, which include untensioned elastic elements, by passing the diaper web between another pair of meshing corrugated rolls. Because the corrugated rolls have their meshing corrugations aligned substantially parallel to the cross-machine direction, incremental stretching of the web takes place in the machine direction. Accordingly, the fully processed legband portions of the diaper web are thereafter elastically extensible in the machine direction, at least to the point of initial stretching.
While Sabee""s suggestion to use corrugated rolls to incrementally stretch a laminate web have been found to work reasonably well when the desired degree of stretching is relatively small, it has been found that for higher degrees of incremental stretching there is a tendency for the corrugated rolls to cause damage to the web. In some situations, this damage can even take the form of rupturing the web potentially rendering the product unsuitable for its intended use. This problem becomes more and more serious as the speed of web processing and the desired degree of incremental stretching increase.
EP 573 587 attempted to solve the aforementioned problem of rupturing the web by sequentially stretching the web during the incremental stretching process. The stretching operation is carried out in stages by passing the web between multiple pairs of meshing corrugated rolls, each pair of rolls exhibiting a greater degree of meshing than the preceding pair, to sequentially stretch the web while minimizing the damage to the web. The use of multiple roll pairs with progressively greater degrees of meshing imposes a lower strain rate on the web than would be the case for a single pair of meshing corrugated rolls having an amplitude and degree of meshing comparable to the final pair of multiple rolls. Minimizing the strain rate reduces the tendency to cause damage to the web.
The problem with both of the above described methods is that the strain rate on the web remains to high and does not permit the desired degree of incremental stretching.
Accordingly, it is an object of the present invention to provide a method for incrementally stretching a web, i.e., activating a web, to a greater degree while minimizing damage to the web.
It is another object of the present invention to provide a method for incrementally stretching a web to a greater degree with less damage than has previously been obtainable with the meshing corrugated rolls of the prior art operating at comparable web speeds.
The present invention is directed to a method and apparatus for activating a web, such as a web of interconnected disposable absorbent articles, such as disposable diapers. The web is fed in a first direction to an activation system comprising a central disc and at least one outer disc. Preferably, the system comprises a central disc and a pair of outer discs. The central disc has a top surface and a pair of opposing side surfaces. At least one of the side surfaces of the central disc comprises at least one activation tool while the outer disc comprises at least one complementary activation tool. Preferably, each of the side surfaces of the central disc comprises an activation tool, more preferably, each of the side surfaces of the central disc comprises a plurality of activation tools. Similarly, it is preferred that each of the outer discs comprise a plurality of complementary activation tools. The web is then folded about the central disc such that a first zone of the web is positioned adjacent the top surface and a second zone of the web is positioned adjacent the side surface. In some embodiments, it may be desired to fold the web about the central disc in a U-like configuration such that a pair of second zones of the web are positioned adjacent the side surfaces of the central disc. The activation tool of the outer disc is engaged with the activation tool of the central disc. The activation tool of the outer disc is disengaged from the activation tool of the central disc. The activated web is then removed from the central disc.
The activation tool of the outer disc may be engaged with the activation tool of the central disc by moving the activation tool of the outer disc inwardly toward the activation tool of the central disc. Alternatively, or in combination with the former, the activation tool of the outer disc may be engaged with the activation tool of the central disc by moving the activation tool of the central disc outwardly toward the activation tool of the outer disc.
The activation tool of the outer disc may be disengaged from the activation tool of the central disc by moving the activation tool of the outer disc outwardly away from the activation tool of the central disc. Alternatively, or in combination with the former, the activation tool of the outer disc may be disengaged from the activation tool of the central disc by moving the activation tool of the central disc inwardly away from the activation tool of the outer disc.
The activation tools preferably comprise corrugations or grooves. Of course other activation tools may be used.